no base gasket with rebuild?

[j753301]

does anybody have any info on using no base gasket for getting correct compression ratio.like what parts are involved exactly.is it only good for bigger bores or can it be done with basicly a stock rebuild?are there any cons when doing this?can sombody help me out please...thanks oh i did do a search and nobody really got into it to deep.

[MATTXR250R]

You need a base gasket...don't assemble the motor without it...They have thinner base gaskets avaliable for some things..like my CR250R..you can a base gasket than is thinner..which I think gives you a bit higher compression ratio..Basically does the samething as it would if you decked the cylinder..using a thinner base gasket is just a cheaper alternative;) :)

[cals400ex]

i run no base gasket along with 2 of my buddies. we all recommend using hondabond on the base. it goes on much smoother than rtv sealant and oil shouldn't break it down. we have all had great luck and i would do it again. just make sure to go lightly with it and do not get it in any of the holes. you don't want to plug oil passages.

[400rednEX]

when it's assembeled you have to end up with enough piston to head and piston to valve clearence. i think the standard is piston .030" in the hole assembeled. you can bolt the cylinder on the case with no base gasket and measure. search for old mickey dunlap posts.

[UglyMotha™]

Originally posted by MATTXR250R
You need a base gasket...don't assemble the motor without it...






noooo you don't NEED a base gasket the jug can be assembled with hondabond on the base and then take the oem head gasket and seperate the three layers and use only one layer and apply high temp spray paint to both sides doin all this quenches the deck hight a minimal amout but like they say every little bit counts doin this mod alone probably won't be noticable but it all adds up

[buster369]

it would work better using the gaskets and shavin some off of the head

[UglyMotha™]

Originally posted by buster369
it would work better using the gaskets and shavin some off of the head



you get into all that and you goin to have to slot your cam sprocket or your timing is goin to be whacked

[buster369]

well u should race my bike that babies got some compression

[UglyMotha™]

you and everybody else too ;)




but yah mines a real slug :huh

[quad_62]

Originally posted by UglyMotha™
take the oem head gasket and seperate the three layers and use only one layer and apply high temp spray paint to both sides doin all this quenches the deck hight a minimal amout

Really? i've never heard of this. ya got me curious.

[Glamis400ex]

WORD OF WARNING.... If you decide to use a RTV or Hondabond for a base gasket, be absolutely sure you are not blocking the oil passage that feeds the cam. I did mine the 1st time with RTV and once I blew a headgasket and tore it down, I realized my oil supply passage to the cam was over 50% plugged. No damage occured, but I only had 4 hours on the 416 rebuild when I blew a gasket. Could have been ALOT worse.

Glamis

[UglyMotha™]

it only takes a film of hondabond to seal not a 1/4 bead if it oozes out the sides then you've got too much

[Teufel]

I would recommend using the gasket and milling the head or decking the cylinder to get your compression ratio. Any RTV that is used is in essence using a gasket. The only way I would consider not using a gasket is if the cases were matched with each other and the cylinder base. JMO

[UglyMotha™]

Originally posted by Teufel
I would recommend using the gasket and milling the head or decking the cylinder to get your compression ratio. Any RTV that is used is in essence using a gasket. The only way I would consider not using a gasket is if the cases were matched with each other and the cylinder base. JMO




mickey stated that he uses the no base gasket method on alot of motors he builds so i'm guessing it really can't be all that bad if a reputible engine builder recomends it and it cost a fraction of the cost of having your head decked


whenever you get the opprotunity read up on this thread

http://www.exriders.com/vbb/showthread.php?s=&threadid=83054&perpage=15&highlight=base%20gasket&pagenumber=2

[Metzroth]

Ok here is what im doing. Do you think this will present any problems? I'm matching the Exhaust port to my new header for better flow. Milling the head (how much should I have it done?). Running it with no base gasket just using thin layer of three bond.
Running two of the 3 layers of the head gasket. Running a higher comp piston (11:1). Can anyone tell me what my actualy compression will be with these mods? Any suggestions or warning send me a PM and post here to let others know.

[Metzroth]

BTW I'm using a ross racing piston. Where is the best place to order from? It's 89mm right? Also what all should i get? I dunno bout milling the head actually. I think I'm just matching the exhaust to the header and using threebond on the base with a thinner head gasket (2 of the 3 layers) and using high temp spraypaint on both sides. With the 11:1 ross pison, what will my actual compression be? cann anyone figure this out for me?
I know there is a compression calculator at www.rosspistons.com
How thick will the head gasket be with only 2 layers and some high temp spray paint. How thick should the super thing layer of threebond me? Should I just run a thin base gasket instead? Anything else I should do to the head while I have it apart? I don't have enuf for a port and polish so should i replace any seals? I need to adjust my valves but I'm going to do that anyways. Is there going to be any timing problems? If so how can i fix them? Any problems with this at all please let me know before I do it. I plan on ordering the parts this weekend. My header is in the mail and as soon as it gets here and i measure the outlet to the silencer I will order the silencer direct from HMF.
By the 18th I want to have all my parts ready. Any little things I'll need? I need oil and .... anything else? Three bond, head gasket, 89mm 11:1 ross piston, feeler guage for valve adjustments, thats all i can think of. Let me know. -Mike

[dork]

make sure you replace the valve seals and while you have the valves out clean the carbon off them.

whether you deck the head, cylinder, or eliminate the base gasket what you're looking for is a .030"-.040" squish clearance. you can measure this by taping 2 pieces of solder (about .065" diameter) on the piston in a cross or X on top of the piston. make sure the ends of the solder are within 1/8" of the cylinder wall. then assemble the head and torque it down, then turn the piston over by hand once and take it apart, then measure the thickness of the solder that was flattened.

running a tighter squish or quench clearance allows higher compression before detonation, provides a cooling effect in the chamber, needs less ignition advance, and mixes the a/f mix better.

you'll retard the cam timing slightly, how much can be determined by degreeing the cam, but it doesn't appear to be a big problem as many riders do this.

[BLEEDRED]

We have been through this so many times before...not a month ago I posted this in a very similar thread. Here it is again...Remember, the bottom line is that you have to do your homework very well before to tear into things. Everybody is going to have a different oppinion and most of them are not right. I went through this same thing a year ago. Read as much as you can before you get started...and remember this is just my oppinion too. Good luck!!



Just to give you an idea of your compression you can go to www.rosspistons.com and click on the compression ratio calculator. On a stock 400EX use these numbers, all numbers are approx, but close:

Bore: 3.346
Stroke: 2.756
Head Volume: 37.2
Gasket Thickness: .035" (head gasket)
Deck Height: .035"
Dome Vol./Valve Pkt.: -1

Now make your adjustments by changing the deck height to reflect removing the base gasket...the stock piston sits about .035" in the hole at true TDC, this is your deck height. The stock base gasket is .020". If you remove the base gasket you can get the deck height down to about .018" (allow about .002" for the hondabond). Use the calc. and see how removing the base gasket will change your compression. Also see what will happen as you change the head gasket thickness.

Remeber to be careful when changing these clearences. It's get super technical when you start talking squish, but it is important to keep everything in mind. You might want to do some more reading. Here are a couple of more things to help...

The Squish Band or "Quench" is defined as that area between
the flat of the piston and the flat of the cylinder head at
top dead center (TDC). On the compression stroke, as the
piston approaches TDC, the compressed mixture of fuel and air
is "squished" to the remaining space of the combustion
chamber where the spark plug and valves reside.
The "squeezing" of the mixture creates turbulence and is
expected to promote a better and more complete combustion.

Deck Height: The distance between the flat "quench" surface
of the piston and the top of the bare cylinder (no head
gasket). Typically an engine is set to zero deck height with
the head gasket (compressed value) defining the "squish band"
value. If the value is negative this indicates the
piston's "quench" surface extends above the top of the bare
cylinder

[Metzroth]

Ok so with a film of threebond and a .20 head gasket will I have enough clearance? I'm probably sending my head to C&D for port&polish and 1mm bigger intake valve and new exhaust valve.

[cals400ex]

i run a 11:1 ross 426 with hondabond and the thin cosmetic flex steel head gasket for the 426. i have had good luck. we had some problems running one layer of the headgasket so i wouldn't recommend that. we had problems blowing it, not serious engine problems.

[BLEEDRED]

Ok so with a film of threebond and a .20 head gasket will I have enough clearance?

You won't know unless you physically measure and run the numbers.

You will probably have plenty of clearence. I run with no base gasket and a .027" head gasket and I still have .048" of squish...which might be a little too much. But I already blew out a head gasket so I don't really want to remove a layer of gasket. It all depends on what piston you are running and how far it sits in the hole at TDC.

[Metzroth]

JE or Ross? I'm staying standard bore. Is cometic flex steel head gasket a good one? Basically I have about $150 left. So I figure 120 for Piston with rings and such ($120 Shipped Hopefully). Then the other 30-40 I can buy my gaskets and threebond. Will I be able to do this? Can anyone figure out the prices for these Items and post up? If I'm missing anything in my list add it in with the price and tell me i missed it. The HMF full i'm getting for an awesome price so I couldn't help but get it :) $113.50 for brand new header and about $189.99 for silencer the fits the Header so you can't go wrong there.

[BLEEDRED]

I have had very good luck with the cometic .027" flex steel gasket...

[Metzroth]

where can i get that head gasket for a stock bore?

[Metzroth]

also is taping the solder to the top of the piston and turning it over once a good way of measuring it? Do you use a Micrometer to measure the solder once its turned over once?

[BLEEDRED]

where can i get that head gasket for a stock bore?

Cometic Gaskets (440)354-0777 The stock bore is an 87MM.



also is taping the solder to the top of the piston and turning it over once a good way of measuring it?

I believe that is the best way. I didn't measure mine that way. I just used a set of callipers and measured how far the piston sat in the hole at TDC (I took a bunch of measurements and then took an average). Then I added the thickness of my head gasket.


Do you use a Micrometer to measure the solder once its turned over once?

Callipers, yes...

[cals400ex]

the stock bore is a 87? i was told that the stock bore and 406's use the stock head gasket size. after that, they make them for your particular bore size. 85mm is the stock size piston.

[BLEEDRED]

85mm is the stock size piston.

You are right 85mm...sorry...I mis-typed!!